Tuesday 6 September 2011

Computational Chemistry, Rouen University, France

Our strategy: a quantum chemical approach in three major steps :
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The analysis of the electronic properties of selected molecular systems requires a quantum
chemical approach. As a first step, we need to validate the method, comparing simulated fluorescence
spectra of already synthesized molecules with experimental ones. In order to avoid time-consuming
calculations, we decided to base all our calculations on density functional theory (DFT), a method of
choice for our problem. In particular, the time-dependent DFT (TDDFT) method produces an
accurate description of excited states, comparable to DFT for the ground state. On the other side,
Franck-Condon and Herzberg-Teller analyses can be used for computing the amplitudes for electronic
transitions from the ground and excited state frequency analyses. For instance, the combination of the
two have been recently employed with success to compute the Herzberg-Teller absorption and
fluorescence spectra of free-base porphyrins.8 It is interesting to mention that solvent effects can be
taken into account.

As a second step, we need to understand the reasons leading to the observed differences in
fluorescence activity between our selected analogues. Different approaches will be envisaged such as
orbital analyses or topological studies of the electron density, both in fundamental and excited states.
Concerning the topological approach, based on the quantum theory of atoms in Molecules (QTAIM),
excited state properties are yet completely unexplored, constituting a real challenge in this field of
quantum chemistry. This information could be of the prime importance to design the next generation
of epicocconone analogues.

In the final step, our validated approach will be used to predict fluorescence properties of the
newly designed series of analogues, guiding experimentalists for new syntheses.

Possible additional tasks:
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1) Reactivity studies:
Mechanisms of some steps involved in the synthesis of these fluorophores, not only from a static 
viewpoint (transition states), but also dynamical. To this aim, the PW-GTO-mixed CP2K code could 
be used to carry out Born-Oppenheimer dynamical simulations. The exploration of these complex 
energy surfaces could be done through a metadynamics approach as pioneered by Laio and Parrinello. 
This method could also provide efficient way of evaluating entropy in solution (cf. Michel and Laio), 
and thus Gibbs energies, enabling a realistic description of the reactivity of such species. 

2)Theoretical developments: 
- new reactivity descriptors within the framework of conceptual DFT 
(from Morells dual descriptor) and QTAIM, applied to fluorescence problems. We are 
currently developping our own parallel code for topological analyses 
- new parameter to quantify the accuracy of TDDFT calculations (for instance, assesment 
and improvement of Tozers  parameter)
-  PCM solvent model and excited states
- implementation and design of fully non-local correlation functionals for van der Waals
interactions (such as Lundqvist, van Voorhis ones)

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Additional information :

Salary : 1850 euros / month (contract for 12 months)

How to apply ? Please contact Prof. laurent Joubert: laurent.joubert@univ-rouen.fr
sending a detailed CV and explaining your motivation for this position.

Laboratory : IRCOF, University of Rouen, France. Group of theoretical chemistry

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